CBS and Down syndrome: The expression of CBS in AMKL is approximately 200-times higher than that in the normal control group, DS cells also contain high H2S levels, which are associated with reduced mitochondrial complex IV activity and ATP generation.67 Thus, CBS/H2S may be involved in the pathogenesis of leukemia in trisomy 21 syndrome and targeting CBS/H2S may provide novel therapeutic approach for leukemia in DS patients.